Though professionally I'm a software developer (firmware for embedded microcontrollers, real-time "hands on hardware" C and Assembly programming) and not a graphics type, I have worked with many graphics related packages, on my own time.

I've started working with Free-CAD, because... it's free, and I have some experience with CSG modeling as part of the .

I'm still getting familiar with the development process, but the attached image shows where I am after one weekend's work.

The model will be a Delaware & Hudson ore hopper, road numbers 101 - 240, built by Bethlehem in 1965, in N scale.